1. Field of the Invention
The present invention relates to a radiation image information reading apparatus for reading radiation image information stored and recorded on a stimulable phosphor sheet and erasing the remaining radiation image information from the sheet.
2. Description of the Related Art
When a certain phosphor is exposed to a radiation, the phosphor stores the energy of the radiation. When the phosphor exposed to the radiation is subsequently exposed to exciting or stimulating rays such as visible light, etc., the phosphor emits accelerated light in proportion to the stored energy of the radiation. The phosphor exhibiting such a property is referred to as a "stimulable phosphor". The stimurable phosphor represented in the form of a sheet is used to record the radiation image information of an object such as a human body thereon and to produce the image information as a visible image. The radiation image information stored and recorded on the stimulable phosphor sheet (hereinafter called merely "sheet") is reproduced as the visible image on a recording medium such as a photographic photosensitive material or on a CRT or the like based on an image signal obtained by photoelectrically reading the accelerated light emitted from the sheet when the sheet is irradiated with the stimulating rays. Then, the sheet from which the radiation image information has been read is illuminated with erasing light emitted from an erasing light source such as a fluorescent lamp, a tungsten lamp or the like, thereby making it possible to erase the radiation image information from the sheet and reuse the sheet.
The apparatus for reading the radiation image information from the sheet on which the radiation image information has been recorded as described above, has generally been known. This type of apparatus normally comprises a cassette holding unit for detachably holding therein a cassette with the sheet stored therein in such a manner that it can be loaded therein and unloaded therefrom, a reading unit for reading the radiation image information in the above-described manner, and an erasing unit for erasing the radiation image information from the sheet after the reading of the radiation image information from the sheet has been completed. In the apparatus referred to above, the sheet, which is stored in the cassette held in the cassette holding unit, is first fed from the cassette to the reading unit, where the radiation image information is read. Thereafter, the sheet is fed to the erasing unit so as to erase the radiation image information therefrom, after which it is fed toward the cassette so as to load the sheet therein again.
In a radiation image information reading apparatus (see Japanese Patent Application Laid-Open No. 63-298333) which has been proposed by the present applicant, for example, an erasing unit is disposed in the course of a sheet feed path used to reciprocatively feed the sheet over the range from the inside of a cassette held in a cassette holding unit to the inside of a reading unit. Then, the sheet in the cassette is allowed to simply pass through the erasing unit along the sheet feed path in a manner as to be fed toward the reading unit. At this time, radiation image information is read from the sheet while the sheet is being fed into the reading unit. After the reading of the radiation image information from the sheet has been completed, the sheet is reversely fed toward the cassette from the reading unit along the sheet feed path so as to be returned to the inside of the cassette. At this time, the radiation image information is erased from the sheet while the sheet delivered from the reading unit is being fed in the erasing unit. In the radiation image information reading apparatus referred to above, the erasing unit is provided between the cassette holding unit and the reading unit. Then, the sheet from which the radiation image information has been read, is reversely fed toward the cassette from the reading unit in order to return the sheet to the cassette. Under this condition, the radiation image information is erased from the sheet. It is therefore possible to prevent the entire structure of the radiation image information reading apparatus from becoming large in size owing to the provision of the erasing unit.
In this type of radiation image information reading apparatus, however, the radiation image information is erased from the sheet after the reading of the radiation image information recorded on the sheet has fully been completed. Thus, the reading of the radiation image information from the sheet and the erasing of the same therefrom are independently carried out. Therefore, a time interval required to read the radiation image information from the sheet and a time interval required to erase it therefrom make a relatively long period of time in total. Accordingly, a long period of time is required until the sheet is enabled to be reused, so that the entire process for reading the radiation image information from the sheet cannot efficiently be carried out.